Significant advances in genetic technology have greatly facilitated our ability to discover novel biological systems. Although this progression continues at a rapid pace, gaining a complete understanding of newly identified systems is sometimes hampered by a lack of appropriate pharmacological tools. Thus, our focus in this R01 application is to develop the pharmacological tools necessary to fully investigate the in vivo functions of the recently discovered neuropeptide S receptor. Neuropeptide S (NPS) is a 20 amino acid peptide that has been linked via its cognate G-protein coupled receptor to a variety of disease states including anxiety, narcolepsy, asthma, obesity, and potentially PTSD. Currently, there is a significant unmet need for non-peptide NPS molecular probes, particularly agonists. Filling this void with potent and selective ligands will expedite discovery of potential therapies that act on the NPS receptor system. Moreover, unlike peptides, small organic molecules are more likely to be systemically bioavailable and penetrate the blood brain barrier. The specific objectives of this application are based on preliminary data obtained during the first year of an R21 proposal to Identify Small Molecules for the Neuropeptide S Receptor. While significant progress has been made toward identifying a core scaffold and delineating a rough NPS antagonist pharmacophore, much development work yet remains. First, there are no known small molecule agonist probes of NPS receptor function. This is significant because a growing body of evidence obtained from i.c.v. injections of the endogenous peptide supports the notion that agonist structures may prove to have a greater number of relevant disease targets than antagonists. Second, the most promising antagonist leads from a drug-like perspective are of moderate potency for at least one of the NPS isoforms (primarily 107N). The current application proposes to continue the synthesis and testing of novel NPS analogs based on our early leads. This approach will provide more drug-like small molecule probes of NPS receptor function and may ultimately lead to pharmacotherapies capable of treating anxiety, narcolepsy, asthma, obesity, or PTSD.